The present invention relates to a method of forming a photographic image of very high contrast using a silver halide photographic light-sensitive material, and more particularly to a stable activator type developing method which can constantly provide an image having good quality in spite of variations in the stirring conditions of the processing solution.
In printing an original of continuous gradation by use of an offset printing plate or the like, the tone is reproduced by a collection of big and small points called "dots". These dots are very minute and are present in a number of 80 to 200 or more per square inch, and moreover they are required to be sharp individually. In the printing industry, therefore, a combination of a lith type light-sensitive material and a lith developer is employed, which enables formation of a dot image of high contrast by a specific development effect called a "lith effect".
The lith developer is an alkaline solution wherein the concentration of a sulfite acting as a preservative is generally controlled to extremely low levels and only hydroquinone is used as a developing agent. When a lith type light-sensitive material is developed with this solution, the tone of the lith type light-sensitive material is generally higher in contrast with a decrease in the concentration of sulfite ions.
However, since the general properties of the lith type light-sensitive material are greatly influenced by the concentration of the developing agent and are sensitive to changes in the concentration of bromine ions, it is difficult to steadily obtain an image of constant quality. Moreover, because of the very low concentration of sulfite ion as preservative in the lith developer, the lith developer after being prepared is very low in its resistance to oxygen in air and it is disadvantageously easily deteriorated.
Furthermore, in continuously processing the lith type light-sensitive material, the bromine ion is released from an emulsion layer and the developing agent is consumed as is the case with typical silver halide light-sensitive materials. Therefore, even if they are supplemented, it is necessary to check and correct the activity of the developer every several hours. This leads to troublesome or complicated daily production control.
In addition, in processing by such conventional methods, a long development time of from 1 minute to 2 minutes at a development temperature of from 25.degree. C. to 35.degree. C. has been needed to obtain sufficient blackening density and dot quality.
Therefore, methods have eagerly been desired which are able to provide dot images of super high contrast and of good dot quality and screen range.
Japanese Patent Application (OPI) No. 22438/76 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") discloses a method in which in order to avoid the use of the unstable lith developer, a hydroquinone based developing agent is introduced in a silver halide emulsion and the processing is carried out by use of an alkaline activator in the presence of a hydrazine compound such as hydrazine sulfate to obtain a negative image of high contrast.
This method improves the stability of the processing solution and accelerates the processing rate. This method, however, has the disadvantages that the dot quality obtained is inferior to those of conventional lith type light-sensitive materials, that dot characteristics suitable for use in the plate-making using a contact screen cannot be obtained, and that the screen range is of too high contrast, although contrast characteristics close to those of the lith type light-sensitive material can be obtained. Moreover, for light-sensitive materials in which hydrazine compounds containing an NH.sub.2 NH-- group have been introduced, it is difficult to hold the contrast characteristics obtained at the beginning of the production of the light-sensitive materials for a long period of time, which is commercially required. This seems due to the vigorous decomposition of the hydrazine compounds with time. Therefore, light-sensitive materials capable of providing images of high contrast cannot be obtained by such a method in which the hydrazine compounds of the type as described above are incorporated in the light-sensitive materials.
U.S. Pat. No. 2,419,975 discloses a method in which a hydrazine compound is added to a silver halide emulsion to obtain a negative image of high contrast. It is described therein that when the hydrazine compound is added to the silver chlorobromide emulsion and the development is carried out using a developer having a pH value as high as 12.8, photographic characteristics of very high contrast, with a .gamma. larger than 10, can be obtained. However, many of the hydrazine compounds as disclosed in this patent are of low stability in the light-sensitive materials and cannot be stored for extended periods of time. Also, for strongly alkaline developers having pH values close to 13, developing agents are easily oxidized by air and unstable, and they cannot be stored or used for extended periods of time. Moreover, the development time is nearly equal to those of conventional lith development. Furthermore, for use in the application of plate-making using a contact screen, such images having only the photographic characteristics of high contrast wherein .gamma. is 10 or more are inferior in dot quality, are of too high contrast in screen range, and therefore are not sufficiently satisfactory.
Hereinafter, the expressions "dot quality" and "screen range" as used herein will be explained in detail.
The expression "dot quality" means the quality of points when the blackening density is converted through a contact screen in the corresponding point area, and, in general, those having low fringe are preferred.
The expression "screen range" indicates the change of the dot area relative to the amount of exposure. Theoretically it is a characteristic to be determined depending on the density pattern of the contact screen used.
Therefore, even by the methods as described in the above cited references, if a contact screen having a density pattern suitable for a light-sensitive material to be used is chosen and used, a desirable screen range can be obtained. However, such choice of the suitable contact screen according to the type of the light-sensitive material used is undesirably very troublesome for those practically engaged in the operation of the plate-making.
Thus it has long been desired to produce light-sensitive materials which permit the formation of good dots, and which have low fringe, by use of a stable processing solution. Furthermore, it has been desired to produce, practically, the same screen range by use of the same contact screen as would be used in the conventional lith development without employing a special operation such as making of determination of an apporopriate contact screen.
In order to overcome the above-described problems, the inventors have developed a method of rapidly obtaining a negative image of high contrast by processing a silver halide light-sensitive material containing an acylhydrazine compound which is stable in the silver halide light-sensitive material and a hydroquinone based developing agent with an alkaline activator solution, as described in Japanese Patent Application (OPI) Nos. 1936/81 and 9743/81. According to this method, an image of good dot quality and screen range is obtained, but it is desired to further improve dot quality. Furthermore, it has been found that according to such method there is a disadvantage in that the dot quality tends to be changed depending on the condition of stirring during processing.